1. Field of the Invention
This invention relates to equipment and a method for measuring the convergence and distance between the floor and the roof of an excavated area, such as in a coal mine.
2. Description of the Related Art
In longwall mining situations it is a practice for extraction of a mineral such as coal to be taken from a seam and whether advance or retreat mining is being worked for the roof of the seam to be allowed to collapse behind the work area. At the face which is being worked, supports are positioned to enable the machinery cutting from the face to have a free run and the supports are advanced as the face advances.
While the collapse of the roof is normally a sudden affair behind the supports there is a natural convergence between roof and floor in the supported region. This effect, of course, varies depending on the material of the roof.